(CNN) -- Four Palestinians were killed, and six were hurt by toxic fumes when Egyptian security forces blew up a tunnel in Rafah, Egypt, the Palestinian Interior Ministry said.

The Egyptians on Wednesday blew up a tunnel on their side of the border with Gaza, Palestinian officials said, but fumes and chemicals from the blast seeped into an adjacent tunnel where the Palestinians were working.

Hundreds of such smuggling tunnels crisscross the border between Egypt and Gaza, providing passage for everything from weapons to humanitarian aid to people. Egyptian and Israeli forces frequently target the tunnels. Egypt has recently begun construction of a steel wall along the border to block such tunnels.